Abstract

We have developed a physical model for the spectral irradiance of 1kW tungsten halogen incandescent lamps for the wavelength range 340–850nm. The model consists of the Planck’s radiation law, published values for the emissivity of tungsten, and a residual spectral correction function taking into account unknown factors of the lamp. The correction function was determined by measuring the spectra of a 1000 W, quartz-halogen, tungsten coiled filament (FEL) lamp at different temperatures. The new model was tested with lamps of types FEL and 1000 W, 120 V quartz halogen (DXW). Comparisons with measurements of two national standards laboratories indicate that the model can account for the spectral irradiance values of lamps with an agreement better than 1% throughout the spectral region studied. We further demonstrate that the spectral irradiance of a lamp can be predicted with an expanded uncertainty of 2.6% if the color temperature and illuminance values for the lamp are known with expanded uncertainties of 20K and 2%, respectively. In addition, it is suggested that the spectral irradiance may be derived from resistance measurements of the filament with lamp on and off.

Figures (7)

Residual corrections, after the spectral irradiances measured at different operating currents have been divided by the blackbody radiance and the emissivity of tungsten. The residual corrections have been normalized in such a way that their average is 1. The solid line is an eighth degree polynomial fitted to the average of the residual corrections.

Ratio of the hot resistance to the room temperature resistance, scaled by T−319K. The resistance ratio was corrected for the contribution of the weakly glowing stem by −0.25%. The uncertainty of this correction is assumed to have a rectangular distribution with a full width of 0.5%. The uncertainty bars correspond to the expanded uncertainties (k=2) of the resistance ratio and temperature measurements.